This invention relates to location of peak pressure (LPP) ignition timing apparatus for an internal combustion engine and particularly for a peak combustion pressure signal processing circuit for use in such apparatus which has the capability of indicating certain information useful for diagnostic services.
An LPP ignition timing control generally includes a plurality of combustion pressure sensors connected by cables to a processing circuit. There are several possible failures of LPP sensor or cables which may affect the operation of the apparatus: an inoperative sensor, a loose connection, a misconnection, a bad cable, etc. In addition, the sensor information provides the opportunity for sensing certain engine malfunctions in the nature of misfire of individual combustion chambers.